Motor cycles primarily have internal combustion engines for their propulsion. Air- or liquid-cooled Otto motors are commonly used, which operate on the two-stroke or four-stroke principle. Diesel motors or Wankel engines are also known. As regards the cylinder arrangement, boxer, in-line or V arrangements with a transversely extending or longitudinal extending crankshaft are used. Single cylinder motors and, with a multi-cylinder arrangement, two to six cylinder motors are known. No motors with a larger number of cylinders have previously been built in mass production due to a lack of space and even six cylinders have up to now appeared only in isolated cases due to their structural size.
In accordance with current technology, motor cycles are provided with motor installations, which can be divided into two basic geometries: In the first case, the crankshaft extends longitudinally with respect to the direction of movement and thus enables the transmission of force via the gearbox to the rear wheel axle via a longitudinally extending driveline (cardan shaft transmission). Only one change in direction of the shaft (90 degrees) directly at the rear wheel is necessary in order to drive the rear wheel and thus a relatively easy and low-maintenance drive, which has low losses, is ensured. In the second case, the crankshaft extends transversely to the direction of movement. This means the transmission of force to the rear wheel with transversely extending shafts, and generally a chain transmission between the gearbox output shaft and the rear wheel. This type of construction achieves the highest degree of efficiency in power transmission and renders a low weight and low manufacturing costs possible but is more maintenance intensive. Constructions in which manufacturing costs are low are, however, more maintenance intensive. Constructions in which power transmission is effected exclusively with shafts without using a chain transmission to the rear wheel with the crankshaft extending transversely to the direction of movement require two changes in direction of the shaft in the shaft transmission sequence, firstly a change of direction (90 degrees) at the gearbox output from transverse to longitudinal (with respect to the direction of movement) to cover the distance to the rear wheel and there again from the longitudinal direction to transverse (90 degrees) to transmit the drive moment to the rear axle. This has a lower efficiency of the drive as a consequence, requires more weight and space and is more expensive to manufacture. This construction is, however, also used due to the greater freedom from maintenance by comparison with chain drives. Examples of chain drives with a longitudinally extending crank shaft are not known in mass production.
With longitudinally extending crankshafts and a multi-cylinder motor construction, it is disadvantageous that conventional arrangements result either in an excessive structural breadth (boxer motors, traditional V motors) or an excessive structural length (e.g. mounting a multi-cylinder inline motor in the longitudinal direction). Furthermore, there are multiple cylinder heads with boxer or V motors. Constructions of this type have been known since the 1920's as also have the associated problems of dimensions and weight.
Transversely extending crankshafts are not convenient for implementing a light, simple and effective cardan transmission. They result, however, when using a chain transmission to the rear wheel, in a favourable weight and the best efficiency in the driveline. Of disadvantage when transversely mounting inline motors is the wide frontal area, which, with an increasing number of cylinders, is at odds with the desired streamline shape and the manoeuvrability of a motor cycle as a result of large lateral distances from the centre of gravity of the vehicle. For this reason e.g. models with transversely extending, six-cylinder inline motors of 750 to 1300 cc capacity from the 1980's from different manufacturers have disappeared from the market without any great success. The maximum common number of cylinders nowadays with transversely extending inline motors for motor cycles is four.
With existing constructions of motor cycle V motors with a transversely extending crankshaft and a large V angle, the structural length in the direction of movement and the necessity of multiple cylinder heads proves to be a disadvantage. Mass produced models of this type are known with two to five cylinders.
Motor cycles have no body work in the manner of a motor car, the motor of which is surrounded over a large area by it. In distinction to a motor car, the outer shape and size of a motor cycle motor influences the aerodynamics and manoeuvrability of a motor cycle very directly as a crucial component of its external shape. Improvements in the field of motor dimensions and weights for motor cycles are therefore of major significance.